Actually, I've been using Xmonad+Gnome for almost a year now and am super happy with it.

If you're willing to leave the false abstraction of stackable "windows" behind in the quest for maximum productivity, I suggest you give it a shot.

In all seriousness, I find it much nicer to use a lightweight WM and install/configure exactly what I need, than have something generic that I don't understand as well (i.e., "desktop environment").